Can we implement ML engine using any general purpose Micro controller?
It depends on what you mean by "ML engine" and whether you want to train models on the uC or just make predictions.  IF you're doing something simple (maybe linear regression, logistic regression, etc.) you might be able to get away with doing training on a uC, especially for small amounts of data.  But you're almost certainly not going to be training deep neural networks on one of those things, at least not in any reasonable amount of time.

OTOH, the "making a prediction part" is usually much cheaper computationally, so if you have a pre-trained model and some prediction engine that can use that model, you could possibly use that on a microcontroller.